It is possible to transmit energy wirelessly between a pair of coil antennas (sometimes known as loop antennas). Typically, a power source is connected to a first antenna (or transmitting antenna) in which current flow induces an electromagnetic field around that antenna. A second antenna (or receiving antenna) in suitable proximity to the first antenna and electromagnetic field may have a current and voltage induced in and across its coils. The second antenna may then be used as a power source for example to charge a battery or to power an electronic device or passive RFID tag. The receiving antenna may be connected to a power converter to output power at a desired rating.
In some applications it may be desirable to maximise the voltage generated across the receiving antenna and it may be possible to do so by matching the positive reactance of the receiving coil with the negative reactance of the power converter, load, or any other associated components. Tuning the reactance or impedance of the receiving coil for a specific application may require manufacture of multiple antennas which can be expensive and time consuming.
It is an object of the present invention to provide an improved coil antenna, or at least to provide the public with a useful choice.